The long fronds or leaves of the Asplenium australasicum form a funnel-shaped nest that gives the plant the nickname ‘bird's nest fern’ or ‘crow's nest fern’. On the frond in the lower middle, as well as on some other leaves, the sori are clearly visible, appearing as brown, fuzzy, diagonal lines, on the underside of the fronds, towards the top.

They produce and contain the spores and in the Asplenium australasicum they are half or more the distance between the frond's midrib and its margin, which distinguish it from the otherwise similar looking Asplenium nidus.